1. Field of the Invention
This invention is a device that automatically provides and maintains any desired amount of pressure within a wide range of pressures over pliant fluid bags with tubular flow outlets thereby providing a simplified effective means of parenteral fluid infusion into patients with minimal supervision on the part of the operator of the device.
2. Background of the Invention
Parenteral infusion of fluids into patients comprises a major subsidiary component of the operational procedures involving the patient not only during surgery but before it in many emergency procedures, and post operatively during recovery periods and thereafter. It is also common knowledge that almost all individuals who have experienced on themselves even the simplest gravity type infusion outside the operating room, have experienced the often dangerous and at least annoying situation, namely the need to beckon the nurse frequently to tend to the infusion device to assure the desired constant flow.
Because the same problem becomes much more acute in the operating room due to the critical dependence of the vitality of the patient on a variety of fluids--such as blood, serum, dextrose--and medications introduced into the patient via such fluids, the problem in this particular operational condition has been attacked by ingenious means described in detail in the following subsection.
The original historical constraint of being forced to infuse fluids in such geographical areas where electrical power did not or could not exist, plus the continued use by physicians of the blood pressure measuring apparata have caused the prime mover of these devices to be limited to the human fist with which pressures in the range of 300 millimeters of mercury can be achieved. Such devices have therefore been so designed as to be dictated by the pressure that only one human fist can product on a rubber ball that fits in the first of one hand leaving the other hand free to manipulate adjustments etc. on these apparata. Even with this constraint of the marriage of the human fist to the all-familiar rubber squeeze ball, ingenious mechanisms have been proposed that use lever arms as in the disclosure of John Vaden Terry in U.S. Pat. No. 3,625,401 or turn handles as in the disclosure of Walter J. Jinotti in U.S. Pat. No. 3,565,292. Notwithstanding that these patent disclosures and several others that shall be described in the following subsection constitute significant contributions to the art, they do suffer from one or more drawbacks that shall be documeted in detail in the following subsection.
A search of prior patents for infusion devices detailed below as well as an analysis of such devices existing in actual use show the absence of completely automatic version of such an infusion device that is also compact and simple to be an operationally practical embodiment for actual use. The reason for this missing link can be traced to the absence of a reasonably thorough quantitative analysis of the interdependences of all of the parameters of such an automatic device in the framework of well established principles and concepts of physics and engineering. The quantitative analysis disclosed herewith, in the section of the detailed description of the invention, is an integral part of the present disclosure and reveals that: due to the specific design that is being disclosed the device has low air volume compression requirements and substantially high pressures can be obtained with a very low horsepower prime mover, for example, a direct current motor of very small dimensions (of the order of one and a half inch in diameter, two inches long) with very low power (fractional horsepower) sufficient for massive as well as normal infusion of fluids. It is also shown in this disclosure that the said miniature compressor can be so designed as to be operated at low RPM for massive infusion and therefore can have sufficiently low noise (sound-noise) to be acceptable for the operating room environment. Without such characteristics of compactness, portability and low noise, an infusion device would not have a wide scope of applicability even if fully automated.
3. Description of the Prior Art
Recent communications in the journals "Anesthesia and Analgesia" and "Anesthesiology" indicate that the Fenwal (registered trademark) infuser and its variants similar to that of U.S. Pat. No. 4,090,514 of Hinck et al are the most commonly used infusers. These same communications, however, point out the drawbacks of these devices. We shall first discuss these communications and then describe a number of patent disclosures on fluid infusers.
Jordan Waldman and Toomas Reband in the journal "Anesthesiology", on pages 73 and 74 of vol. 50, in January 1979 point out that "conventional hand-bulb cylinders or pressurized bags for infusing blood rapidly are unsatisfactory when rapid, constant flow infusion is desired." They refer to the Fenwal infuser which is a pliant inflatable bag to which another layer of cloth is attached in such a way as to be able to insert the fluid bag between the bag and the cloth and apply pressure on the fluid bag by use. The reason for this missing link can be traced to the absence of a reasonably thorough quantitative analysis of the interdependences of all of the parameters of such an automatic device in the framework of well established principles and concepts of physics and engineering. The quantitative analysis disclosed herewith, in the section of the detailed description of the invention, is an integral part of the present disclosure and reveals that: due to the specific design that is being disclosed the device has low air volume compression requirements and substantially high pressures can be obtained with a very low horsepower prime mover, for example, a direct current motor of very small dimensions (of the order of one and a half inch in diameter, two inches long) with very low power (fractional horsepower) sufficient for massive as well as normal infusion of fluids. It is also shown in this disclosure that the said miniature compressor can be so designed as to be operated at low RPM for massive infusion and therefore can have sufficiently low noise (sound-noise) to be acceptable for the operating room environment. Without such characteristics of compactness, portability and low noise, an infusion device would not have a wide scope of applicability even if fully automated.
3. Description of the Prior Art
Recent communications in the journals "Anesthesia and Analgesia" and "Anesthesiology" indicate that the Fenwal (registered trademark) infuser and its variants similar to that of U.S. Pat. No. 4,090,514 of Hinck et al are the most commonly used infusers. These same communications, however, point out the drawbacks of these devices. We shall first discuss these communications and then describe a number of patent disclosures on fluid infusers.
Jordan Waldman and Toomas Rebane in the journal "Anesthesiology", on pages 73 and 74 of vol. 50, in January 1979 point out that "conventional hand-bulb cylinders or pressurized bags for infusing blood rapidly are unsatisfactory when rapid, constant flow infusion is desired." They refer to the Fenwal infuser which is a pliant inflatable bag to which another layer of cloth is attached in such a way as to be able to insert the fluid bag between the bag and the cloth and apply pressure on the fluid bag by inflating the infuser bag, thus squeezing the fluid bag between the infuser bag and the said attached cloth; a variant of this is disclosed in U.S. Pat. No. 4,090,514 by Hinck et al where the secondary "cloth" is made of two pieces with Velcro (trademark) type means for locking the two pieces of the additional enveloping portion that go around the fluid bag. Waldman and Rebane suggest the use of pressurized gas, in place of air or gas from the hand squeezed hand-bulb, that is to be obtained from wall oxygen in the hospital or from pressurized gas cylinders plus a pressure-flow regulator. In answer to this suggestion, James S. Hicks suggest in "Anesthesiology", vol. 51, in October 1979, on page 364, the use of the "orthopedic tourniquet system" driven by oxygen cylinder when massive, rapid infusion of blood is necessary, with the tourniquet attached to the Fenwal pressure bag line. In addition to these suggestions, L. Brian Ready discusses in "Anesthesia and Analgesia", vol. 58, in March-April 1979, on page 155, the need for rapid intravenous infusion, "a means of maintaining a rapid infusion rate without the need for repeated manual inflation of a blood pump". He suggests the use of an "automatic tourniquet" in conjunction with the Fenwal bag, but Alan Jay Schwartz, David R. Jobes and Norig Ellison, in response to this suggestion also point out in "Anesthesia and Analgesia" in vol. 59, March 1980, on page 226, that while Ready's suggestion is a good one, they "have experienced one occasion where the bulging seam of the plastic bag containing heparin solution split, resulting in a shower of solution of the operating field, the anesthesia machine and the adjacent personnel. Fortunately, the bag was heparin, not a transfusion". There is further evidence that the same has happened with blood.
In addition to controlled pressure, a constant high pressure is needed for aiding surgery by the infusion of cardio-plegic solution during cardio-vascular/open heart operation or procedure.
Thus the need for a completely self-contained compact unit with a very carefully controlled pressure that is constant in time and over the whole fluid bag, that does not rely on high pressure gases from gas cylinders or from wall gas outlets of a hospital is established.
Study of previous inventions of pressure infusion devices, to be described below, can be summerized as variants of four principle methods of application of pressure: (1) "Bag on bag" method as that of Howard Helmut Hinck et al (U.S. Pat. No. 4,090,514) and that of Bede Stanislaus Nugent (U.S. Pat. No. 3,895,741); (2) "Rigid movable wall on bag" advanced, for example, by a screw-spring system as that of Walter J. Jinotti (U.S. Pat. No. 3,565,292) or of John Vaden Terry (U.S. Pat. No. 3,625,401); (3) "Squeeze out" type as that of Ellis Whiteside Clarke (U.S. Pat. No. 3,949,744) or variants of it such as the I.V. STAT (trademark) that incorporates a spring loading mechanism for squeezing out; (4) Related fluid dispensing methods such as that of Albert R. Uhlig (U.S. Pat. No. 4,147,278) which can be briefly described as "Air on a bag in rigid container".
The Hinck type infuser (which is a variant of the commonly used Fenwal device mentioned earlier), in addition to being first operated (and therefore not automatic), uses a Velcro fastener for the envelope that encases the fluid bag. It suffers from the same problems of uncontrolled pressure (causing bursting) as well as the Velcro fastener becoming inactive due to capture of lint etc. in the operating room environment. The Nugent version is specifically designed to prevent infusion of gas trapped in the fluid bag, by allowing the gas to rise to the upper part of the bag. The same result can be achieved with a rigid wall type infuser as well. It also has introduced an operable door concept which is useful. Otherwise, this device also has the same disadvantages as the Hinck one in so far as pressure control is concerned.
Of the rigid but moveable wall type infusers, the Jinotti device does not provide a constant pressure on the fluid bag because it uses Hooke's Law (using a spring loading), i.e. force=the spring constant times the displacement; therefore as the bag becomes depleted, and the spring extends back from where it was compressed to, the force (and therefore the pressure) on the bag changes. Even if a variant of it is designed so as to be able to readjust the force on the spring by recranking the screw, it will still require repeated intervention by the operator. Furthermore if a nonlinear spring is designed so as to provide a constant pressure, the spring will provide only a particular pressure and will not provide a wide range of variably controlled pressures for infusion of different fluids nor for infusion of any given fluid at different flow rates.
The Terry device is mechanically too complicated for practical use. It uses liquid-fluidic components interspersed with pulleys, strings and lever arms. It is intrinsically slow because it uses liquid fluidics as opposed to gas, and furthermore the fluidics used is not in the modern sense which has been recently developed to simulate electronic components such as amplifiers. Therefore, it is impractical for rapid, repetitive sequential application of the device for massive infusion.
The Clarke device is singularly disadvantageous for rapid massive infusion because it has no quantitative control on the pressure and requires constant attention by the operator. In conjunction with this device there is a variant, namely the I.V. STAT, that has been discussed above.
In many of the devices mentioned above, a spring is used in conjunction with a piston for the main purpose of providing pressure derived from the potential energy stored within the spring; we note that in the present disclosure a spring is also used but for the sole purpose of pressure-free retraction of such a piston and therefore a spring having a negligable spring constant can be used; this point is discussed further in the disclosure.
Because the present device will allow operation at pressures much higher than those used up to now, it is expected that previous designs of fluid bags such as that of Albert Frank Bujan et al (U.S. Pat. No. 3,915,212) may be modified to withstand higher pressures for much more rapid infusion for critical uses.
It is also to be expected that the presently disclosed device will open up opportunities for the development of new types of blood filters that can be used in conjunction with massive infusion applications at high pressures.